This invention relates to heat exchangers, and more particularly, to baffles employed in heat exchangers.
Recent years have seen an explosion in the popularity of so-called xe2x80x9cparallel flowxe2x80x9d heat exchangers. One typical construction is illustrated in U.S. Pat. No. 4,688,311 issued Aug. 25, 1987 to Saperstein, et al.
Heat exchangers of this sort have been employed in a variety of applications including condensers and evaporators in air conditioning and refrigerating systems and in oil coolers which are employed to cool lubricating oil or hydraulic fluid, particularly in vehicular applications. Indeed, there is suggestion in the prior art that parallel flow heat exchangers even be employed as radiators for cooling engine coolant in vehicles.
Modern day parallel flow heat exchangers are typically made of aluminum and employ two spaced tubular headers. Flattened tubes extend between and are in fluid communication with the interiors of the headers. Serpentine fins are located between the flattened tubes.
Conventionally, aluminum is the material of choice and the result is a compact, lightweight heat exchanger which operates with exceptional efficiency particularly when the hydraulic diameter of the fluid passageways within the flattened tubes is 0.070xe2x80x3 or less.
In many applications, it is desired that the fluid contained within the heat exchanger make more than one pass through the heat exchanger across the cooling air path in which the heat exchanger is disposed. To achieve this, it is conventional to locate one or more baffles in one or both of the headers to achieve as many passes as is desired.
Typically, the baffles have been plate-like inserts that are disposed in slits in the headers. To seal the slits as well as the point of contact of the baffle with the interior of the header, when the materials employed are aluminum reliance is made on the flow of braze alloy to seal any voids. The use of slits in the headers may tend to weaken the headers and, in some instances, may result in a significant number of leaky headers being formed as a result of fluid pressure within the headers that result from the application of heat to the heat exchanger during the brazing process.
In other cases, cap-like baffles have been inserted endwise into the headers to the desired location and then brazed in place. While such baffles usually are quite leak free, this method of installation does not lend itself to use with a header whose interior cross section may vary.
U.S. Pat. No. 4,615,385 issued Oct. 7, 1986 to Saperstein, et al., there is disclosed a unique header for heat exchangers of this type. To provide improved strength in the resulting heat exchanger, each header is formed of a generally cylindrical tube with a series of tube slots formed in one side thereof. Between each tube slot, a dome is formed, which dome is in the shape of a compound curve. Because of the use of the domes between adjacent tube slots, stresses at the tube to header joints in the resulting heat exchangers are considerably reduced and a much stronger heat exchanger results.
However, because of the use of the domes, the cross section of the header is relatively large where each dome is formed and is relatively smaller where each tube slot is formed. As a consequence, it has heretofore been impossible to provide such headers with baffles that are inserted endwise into the headers.
The present invention is directed to overcoming one or more of the above problems.
It is the principal object of the invention to provide a new and improved method of providing a header with an interior baffle. More specifically, it is an object of the invention to provide a new and improved method of installing a baffle in a tubular header.
It is also an object of the invention to provide a heat exchanger that includes a header provided with a baffle in accordance with the process or method of the invention.
Still another object of the invention is to provide a novel baffle preform that may be used in practicing the method of the invention.
An exemplary embodiment of a method of installing a baffle in a tubular header for a heat exchanger includes the steps of: (a) providing a baffle with a concave side periphery smaller than the internal periphery of the header; (b) locating the baffle at a desired location within the header; and (c) applying a compressive force to the baffle to compress the baffle toward a planar shape.
As a result of the foregoing, the baffle expands peripherally within the header to engage the interior of the header whereat it may be secured and sealed as, for example, but not necessarily, by brazing.
In one embodiment of the method, the baffle is concavo-convex has a generally circular periphery and includes a generally central convex dome surrounded by a peripheral, radially outward directed skirt.
In a highly preferred embodiment of the invention, both the header and the baffle are aluminum and the baffle is braze clad on both sides thereof.
In one embodiment of the invention, step (b) is performed by placing the header over a spindle and abutting it against a stop and then placing the baffle within the header in abutment with the spindle.
In one embodiment of the invention, step (c) is performed by placing a second spindle within the header after the performance of step (b) and moving the second spindle against the baffle and towards the first-named spindle.
In one embodiment of the invention, step (b) is preceded by the step of sizing the interior of the header at the desired location of the baffle.
Preferably, the step of sizing is performed by locating an expandable mandrel within the header at the desired location and expanding the mandrel into the header at the desired location.
In a highly preferred embodiment of the invention, the expandable mandrel is a split mandrel and the step of expanding the expandable mandrel is performed by moving a wedge into the split mandrel.
In one embodiment of the invention, there is provided a heat exchanger that includes a header with a baffle therein and which is made according to the process described above.
According to another facet of the invention, a baffle preform is provided for use in the manufacture of a heat exchanger with a baffled, tubular header. The baffle preform comprises a metallic slug having a convex side and an opposite concave side. The slug is circular and has a generally semi-spherical dome of smaller diameter than the slug on one side thereof and a radially outward directed skirt extending from the base of the dome to the periphery of the slug.
Preferably, the skirt is frustoconical.
In a highly preferred embodiment, the minor base of the skirt merges into the base of the dome and the skirt also extends axially away from the dome.
Preferably, the slug is formed of aluminum sheet and is braze clad on both sides thereof.
The invention also contemplates a method of making a heat exchanger header with an internal baffle which comprises the steps of (a) providing a tubular header of generally cylindrical shape and having a series of tube receiving slots at one side thereof which are separated by domes shaped as compound curves, the cross section of the header being relatively larger at the domes and relatively smaller at the tube slots; (b) providing a concave baffle of a generally circular periphery, and of a diameter sufficiently small so as to be received in the header and located therein generally transverse thereto at the relatively larger cross section and of a diameter larger than the relatively small cross section; (c) locating the baffle within the header at a desired one of the domes; (d) causing the baffle to be generally transverse to the header; and (e) collapsing the baffle to a generally planar configuration at the desired one of the domes.
Preferably, step (e) is performed by relatively moving mandrels on opposite sides of the baffle towards each other.
Preferably, step (b) is performed by providing a baffle of sheet-like material having a dome surrounded by a generally radially outward directed skirt.
In this embodiment, the dome is generally semispherical and preferably, the skirt is generally frustoconical.
Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings.